WWII Science & Technology: The Race That Changed Everything - Part 5: Radar vs. the Atomic Bomb: The Weapon That Actually Won the War

The Invisible Victory

Ask anyone what technology won World War II, and they’ll probably say: the atomic bomb.

It’s wrong. The atomic bomb ended the war. Radar won it.

The atomic bomb was used exactly twice, in the final week of a war that was already decided. Radar was used every single day, on every front, from 1940 to 1945.

But radar doesn’t make for good movies. There’s no mushroom cloud, no Dr. Strangelove, no moral anguish. Just phosphorescent screens and drowsy operators and the slow, unglamorous work of not being surprised.

What Radar Did

Let’s be specific about what radar accomplished:

1. Won the Battle of Britain

In the summer of 1940, the Luftwaffe attempted to destroy the Royal Air Force as a prelude to invasion. They outnumbered the British significantly. They should have won.

They didn’t, because Chain Home radar gave the British something they’d never had before: early warning.

RAF controllers knew where German formations were before they crossed the Channel. They could concentrate defensive fighters at the point of attack instead of dispersing them across the entire coast.

“Without radar, the Battle of Britain would have been lost.”
— Air Chief Marshal Hugh Dowding

2. Defeated the U-Boat Threat

German submarines nearly won the war by starving Britain into submission. In early 1942, U-boats were sinking Allied ships faster than they could be built.

The turning point was airborne microwave radar. Aircraft equipped with it could detect submarine periscopes from miles away. U-boats that had hunted on the surface now had to hide—which meant they couldn’t find convoys either.

3. Enabled Strategic Bombing

The thousand-bomber raids over Germany weren’t possible without radar. H2S ground-mapping radar let bombers navigate at night and through clouds. Pathfinder aircraft used radar to mark targets for following waves.

4. Won the Pacific Air War

American radar in the Pacific detected Japanese attacks before they arrived. At the Battle of the Philippine Sea, radar-guided fighters shot down so many Japanese planes that Americans called it “The Great Marianas Turkey Shoot.”

5. Enabled D-Day

The Normandy invasion required total air and sea superiority over the landing beaches. Radar provided both: detecting any German aircraft that approached and directing naval gunfire against shore targets.

The Cavity Magnetron: The Most Important Object of the War

All radar is not created equal.

Early radar used long wavelengths that couldn’t detect small objects or be mounted in aircraft. The breakthrough was the cavity magnetron—a device that generated microwaves powerful enough for practical radar.

The British invented it in February 1940. Two physicists at Birmingham University, John Randall and Harry Boot, created a device no bigger than a man’s fist that could produce kilowatts of microwave power.

The implications were revolutionary:

• Submarine detection: Small enough for aircraft
• Precision bombing: Could map ground features
• Fire control: Accurate enough to aim guns
• Night fighting: Could track individual aircraft

But Britain in 1940 couldn’t manufacture it at scale. Industry was committed to basic war production. The country was under siege.

So they gave it away.

The Tizard Mission: Britain’s Greatest Gift

In September 1940, a small British delegation arrived in Washington carrying a black metal box. Inside was a cavity magnetron—along with designs for jet engines, rockets, and nuclear research.

This was the Tizard Mission (more on this in a future post). Its purpose: share Britain’s most advanced technology with America in exchange for industrial production.

The Americans were stunned. The cavity magnetron was so far ahead of their own radar research that engineers initially didn’t believe it worked.

Within months, MIT had established the Radiation Laboratory (deliberately misnamed to hide its true purpose) dedicated to microwave radar. By 1945, the Rad Lab had spent $2.5 billion—as much as the entire British war budget—on radar development.

“When the war is over, the magnetron will be seen as one of the most important inventions in history.”
— American radar engineer, 1941

Why We Forgot Radar

The atomic bomb is remembered because it was dramatic. A single weapon destroyed a city. The moral questions are vivid. The imagery is unforgettable.

Radar prevented destruction. It stopped attacks before they succeeded. It found submarines before they sank ships.

There’s no memorial to the convoys that arrived safely because airborne radar spotted the U-boats. No photographs of the bombers that weren’t shot down because night fighters couldn’t find them.

Radar’s victories were invisible. And invisible victories don’t make history books.

The Counterfactual

Consider what happens without radar:

1940: Britain loses the Battle of Britain. Without early warning, the RAF is destroyed on the ground. Germany invades or forces a negotiated peace. America has no base for European operations.

1942: U-boats win the Atlantic. Britain starves. No Lend-Lease reaches the Soviet Union. No American buildup in Europe is possible.

1943: Strategic bombing campaign fails. Without navigation and targeting radar, bombers hit fields instead of factories. Germany’s industrial capacity is unaffected.

1944: D-Day is impossible. Without air superiority over the Channel, the invasion fleet is slaughtered.

1945: There is no 1945 victory. The war continues indefinitely, or Germany develops its own atomic bomb first.

The atomic bomb ended a war that was already won. Radar made victory possible.

The Technology Itself

For those interested in the engineering, here’s what made radar work:

Basic principle: Radio waves reflect off objects. Measure the time between transmission and return, and you know the distance. Measure the direction of the returning signal, and you know where the object is.

The problem: Long wavelengths meant poor resolution. You couldn’t distinguish between a bomber and a flock of birds.

The solution: Microwaves. Shorter wavelengths meant tighter beams and better resolution. But generating powerful microwaves required new physics—which the cavity magnetron provided.

The cavity magnetron: Electrons spiraling in a magnetic field generate oscillating electromagnetic radiation. Cavities in a copper block amplify specific frequencies. The result: kilowatts of microwave power from a device you could hold in your hand.

The Unsung Heroes

Radar was invented by multiple people in multiple countries nearly simultaneously:

• Robert Watson-Watt (Britain): Led Chain Home development
• Christian Hülsmeyer (Germany): Patented radar principles in 1904
• Albert Taylor & Leo Young (USA): Demonstrated radar in 1922
• Émile Girardeau (France): Developed ship radar
• John Randall & Harry Boot (Britain): Invented the cavity magnetron

But the British made it work first, made it work at scale, and then shared it with the Americans who mass-produced it.

The Legacy

Radar didn’t disappear after WWII. It evolved into:

• Air traffic control: Every modern airport
• Weather forecasting: Doppler radar
• Automotive safety: Collision avoidance
• Astronomy: Radio telescopes
• Medicine: Medical imaging technologies

The microwave oven in your kitchen is a direct descendant of cavity magnetron research. (Engineers noticed that radar equipment heated things up. One experimenter accidentally melted a chocolate bar in his pocket.)

The Lesson

The atomic bomb teaches a simple lesson: technology can destroy cities.

Radar teaches a more subtle one: the most important technologies are often invisible.

We notice the things that cause spectacular destruction. We don’t notice the things that prevent it. The submarine that doesn’t find the convoy, the bomber that doesn’t reach the city, the invasion that doesn’t happen—these are history’s greatest victories, and they leave no monuments.

When people ask what technology won WWII, remember the operators staring at phosphorescent screens in darkened rooms, watching blips move across the Atlantic, vectoring aircraft to intercept.

That’s what victory looks like. Not a mushroom cloud—but a submarine turning away because it knows it’s been seen.

This post is part of the WWII Science series, exploring how wartime pressures transformed technology and ethics forever.